A conventional car navigation device includes a function of playing back music recorded in a CD (Compact Disc) or the like in many cases. Further, many car navigation devices have a function of outputting, by voice, information including information about a route to a destination, traffic information, and information showing an approach to a recommended spot, a registered point, or an attention point (each information outputted by the navigation devices, other than music, is generically referred to as “guidance information” from here on).
A problem with a car navigation device having both these functions is that when output of guidance information by voice is performed simultaneously with a playback of music, the two sounds coincide. Audio information, such as guidance information or music which a navigation device outputs, is generically referred to as an “audio output.”
In order to solve this problem, patent reference 1 discloses a technique of providing road traffic information during an interlude portion of a musical piece. In more detail, guidance information is played back during an interlude of a musical piece (a portion other than vocals), and, at a time when a vocal part is played back after returning to the musical piece, a return to the beginning of the vocal part is performed and this part is played back.
Further, patent reference 2 discloses a technique of controlling the playback of pieces of music by predicting a point which traffic information will be received in advance, and then changing the order of the playback list in such a way that pieces of music are completed until then.